Permanent Weight Paint
The problem is you have to edit your vertex group. 


go into edit mode and hit the vertex groups tab. 
then see all of you vertex group and experiment by means of randomly selecting vertex groups by clicking the 'select' tab while in the vertex groups sections in the properties window.
when you see a mesh that has vertices scattered and not in the location you want them to be, click 'remove' tab so blender will erase all vertices that were assigned to that group.
next group the vertices that you want to  be grouped(do it logically).


ex: hand vertices grouped, then called 'hand verts'. Head vertices grouped and called 'head verts'(or whatever you prefer).


now that your veticies are logically grouped, go into weight paint mode and commence weight painting again. (your problem should be fixed).


p.s update me if that doesn't work, or if your having issues.

happy blending!